Fair Values of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Securities Available for Sale: [Abstract]
Securities Available for Sale	$ 1,191,107	$ 1,244,619
Trading Securities	3,851	3,062
Financial assets
Net loans	4,251,119	3,800,203
Financial liabilities
Time deposits	1,018,957	933,127
Long-term debt	367,144	370,344
Trust preferred debentures	75,422	75,422
Fair Value, Inputs, Level 2 [Member] | Carrying Amount [Member]
Financial assets
Securities held to maturity	61,302	70,811
Financial liabilities
Time deposits	1,018,957	933,127
Long-term debt	367,144	370,344
Fair Value, Inputs, Level 2 [Member] | Estimated Fair Value [Member]
Financial assets
Securities held to maturity	62,401	72,198
Financial liabilities
Time deposits	1,028,110	942,437
Long-term debt	418,349	427,107
Fair Value, Inputs, Level 3 [Member] | Carrying Amount [Member]
Financial assets
Net loans	4,180,385	3,728,869
Financial liabilities
Trust preferred debentures	75,422	75,422
Fair Value, Inputs, Level 3 [Member] | Estimated Fair Value [Member]
Financial assets
Net loans	4,298,990	3,821,640
Financial liabilities
Trust preferred debentures	57,123	55,980
Fair Value, Measurements, Recurring [Member]
Securities Available for Sale: [Abstract]
U.S. Treasury	64,662	82,233
Federal Agency	296,158	255,846
State & municipal	92,504	104,789
Mortgage-backed	279,596	325,397
Collateralized mortgage obligations	446,887	465,475
Other securities	11,300	10,879
Securities Available for Sale	1,191,107	1,244,619
Trading Securities	3,851	3,062
Interest Rate Swaps	1,490
Total	1,196,448	1,247,681
Liabilities:
Interest Rate Swaps	1,490
Total	1,490
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities Available for Sale: [Abstract]
U.S. Treasury	64,662	82,233
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	9,210	8,825
Securities Available for Sale	73,872	91,058
Trading Securities	3,851	3,062
Interest Rate Swaps	0
Total	77,723	94,120
Liabilities:
Interest Rate Swaps	0
Total	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Securities Available for Sale: [Abstract]
U.S. Treasury	0	0
Federal Agency	296,158	255,846
State & municipal	92,504	104,789
Mortgage-backed	279,596	325,397
Collateralized mortgage obligations	446,887	465,475
Other securities	2,090	2,054
Securities Available for Sale	1,117,235	1,153,561
Trading Securities	0	0
Interest Rate Swaps	1,490
Total	1,118,725	1,153,561
Liabilities:
Interest Rate Swaps	1,490
Total	1,490
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Securities Available for Sale: [Abstract]
U.S. Treasury	0	0
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	0	0
Securities Available for Sale	0	0
Trading Securities	0	0
Interest Rate Swaps	0
Total	0	0
Liabilities:
Interest Rate Swaps	0
Total	$ 0